Slip Detection And Mitigation For An Electric Drive Powertrain Having A High Ratio Traction Drive Transmission

ABSTRACT

A method of controlling a continuously variable electric drivetrain (CVED) including a high ratio traction drive transmission and at least one of a first motor-generator and a second motor-generator is disclosed. The method includes the steps of receiving a an output speed, determining a kinematic output speed, and determining a slip state of the high ratio traction drive transmission based on a comparison of the output speed to the kinematic output speed.

CROSS-REFERENCE TO RELATED APPLICATION

The present patent application claims the benefit of U.S. ProvisionalPatent Application No. 62/733,872, filed on Sep. 20, 2018, which isfully incorporated herein by reference in its entirety.

BACKGROUND

Electric and hybrid electric vehicles are enjoying increased popularityand acceptance due in large part to the cost of fuel and greenhousecarbon emission government regulations for internal combustion enginevehicles. Hybrid vehicles include both an internal combustion engine aswell as an electric motor to propel the vehicle.

In current electric axle designs for both consuming as well as storingelectrical energy, the rotary shaft from a combination electricmotor-generator is coupled by a gear train to the driven wheels of thevehicle. As such, the rotary shaft for the electric motor-generator unitrotates in unison with the wheel based on the speed ratio of the geartrain. Powertrains implementing electric motors are faced with a largespeed reduction between the electric motor and the driven wheels. Insome cases, electric machines having high rotational speeds, for examplehigher than 30,000 rpm, are being considered for implementation in avariety of powertrain configurations. It is appreciated that traditionalgearing structures with high transmission ratios, for example those withtransmission ratios in the range of 25-40, are needed for implementationof high speed electric machines. Traditional toothed gearing havingtransmission ratios in said range are prohibitively expensive tomanufacture and often are prohibitively noisy during operation.

Accordingly, it would be desirable to develop a method of controlling anelectric drivetrain which enhances efficiency and accuracy, while costthereof is minimized.

SUMMARY

In concordance and agreement with the present disclosure, develop amethod of controlling an electric drivetrain which enhances efficiencyand accuracy, while cost thereof is minimized, has surprisingly beendiscovered.

In one embodiment, a method of controlling an electric drivetrain,comprises: providing a traction drive transmission including a ringmember, a carrier having a plurality of traction members, and a sunmember; and determining a slip state of the traction drive transmissionbased on a comparison of a speed of at least one of the ring member, thecarrier, the plurality of traction members, and the sun member to akinematic speed of the at least one of the ring member, the carrier, theplurality of traction members, and the sun member.

As aspects of certain embodiments, the traction drive transmission isoperably coupled to at least one motor-generator.

As aspects of certain embodiments, the method further comprisesswitching the at least one motor-generator from a torque-control mode toa speed-control mode in order to mitigate the slip state.

As aspects of certain embodiments, the method further comprisesmitigating the slip state of the traction drive transmission byadjusting a speed of the at least one motor-generator.

As aspects of certain embodiments, the method further comprisesswitching the at least one motor-generator from the speed-control modeto the torque-control mode once the traction drive transmission is nolonger in the slip state.

In another embodiment, a method of controlling a continuously variableelectric drivetrain, comprises: providing a first motor-generator, asecond motor-generator, and a high ratio traction drive transmissionhaving a ring member, a carrier configured to support a plurality oftraction members, and a sun member, wherein one of the ring member, thecarrier, and the sun member is operably coupled to the firstmotor-generator, wherein one of the ring member, the carrier, and thesun member transmits a rotational power, and wherein one of the ringmember, the carrier, and the sun member is operably coupled to thesecond motor-generator; measuring a speed of at least one of thecarrier, the ring member, the sun member, the first motor-generator, andthe second motor-generator; determining a kinematic speed of at leastone of the carrier, the ring member, the sun member, the firstmotor-generator, and the second motor-generator based on the speed of atleast one of the first motor-generator and the second motor-generator;and determining a slip state of the high ratio traction drivetransmission based on a comparison of the measured speed of at least oneof the carrier, the ring member, the sun member, the firstmotor-generator, and the second motor-generator to the kinematic speedof at least one of the carrier, the ring member, the sun member, thefirst motor-generator, and the second motor-generator.

As aspects of certain embodiments, the method further comprisesdetermining a ring slip based on a comparison of the speed of the ringmember to the speed of the at least one of the first motor-generator andthe second motor-generator.

As aspects of certain embodiments, the method further comprisesdetermining a sun slip based on a comparison of the speed of the sunmember to the speed of the at least one of the first motor-generator andthe second motor-generator.

As aspects of certain embodiments, the method further comprisescommanding a change in the speed of the at least one of the firstmotor-generator and the second motor-generator based on the ring slip.

As aspects of certain embodiments, the method further comprisescommanding a change in the speed of the at least one of the firstmotor-generator and the second motor-generator based on the sun slip.

As aspects of certain embodiments, the method further comprisescommanding a change in a power ratio between the first motor-generatorand the second motor-generator based on the slip state.

As aspects of certain embodiments, wherein commanding the change in thepower ratio includes adjusting the speed of at least one of the firstmotor-generator and the second motor-generator.

In yet another embodiment, a method of controlling a continuouslyvariable electric drivetrain, comprises: providing a motor-generator anda high ratio traction drive transmission including a sun member, acarrier configured to support a plurality of traction members, a ringmember in contact with the traction members, wherein at least one of thering member, the carrier, and the sun member is operably coupled to themotor-generator, wherein at least one of the ring member, the carrier,and the sun member transmits a rotational power, and wherein at leastone of the ring member, the carrier, and the sun member is caused toremain stationary; measuring an output speed of the continuouslyvariable electric drivetrain; determining a kinematic output speed ofthe continuously variable electric drivetrain based on a ring-to-sunratio of the high ratio traction drive transmission; and determining aslip state of the high ratio traction drive transmission based on acomparison of the output speed to the kinematic output speed.

As aspects of certain embodiments, the method further comprisesmitigating the slip state of the high traction drive transmission byadjusting a speed of the motor-generator.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are incorporated herein as part of thespecification. The drawings described herein illustrate embodiments ofthe presently disclosed subject matter, and are illustrative of selectedprinciples and teaching of the present disclosure and do not illustrateall possible implementations thereof. The drawings are not intended tolimit the scope of the present disclosure in any way. A betterunderstanding of the features and advantages of the present embodimentswill be obtained by reference to the following detailed description thatsets forth illustrative embodiments, in which the principles of thepreferred embodiments are utilized, and the accompanying drawings ofwhich:

FIG. 1 is a cross-sectional view of a simplified high ratio tractiondrive transmission having a tapered roller;

FIG. 2 is a cross-sectional view of an embodiment of a high ratiotraction drive transmission of an offset traction roller transmissiontype;

FIG. 3 is a cross-section plan view of the offset-type traction rollertransmission of FIG. 2;

FIG. 4 is a cross-sectional view of an embodiments of a high ratiotraction drive transmission of a tapered planetary traction rollertransmission type;

FIG. 5 is a schematic illustration of an electric axle having acontinuously variable electric drivetrain;

FIG. 6 is a lever diagram of yet another embodiment a continuouslyvariable electric drivetrain having two motors and a high ratio tractiondrive transmission;

FIG. 7 is a variogram showing the range of possible vehicle speeds andaxle torques as a function of motor speeds for a representativeconfiguration of the above embodiments;

FIG. 8 is a flow chart depicting a control process that is used forcontinuously variable electric drivetrains having two motors and a highratio traction drive transmission;

FIG. 9 is a table depicting a number of diagnostic states forcontinuously variable electric drivetrains having two motors and a highratio traction drive transmission;

FIG. 10 is a chart depicting power ratio and torque ratio versus timeduring slip mitigation for a continuously variable electric drivetrainhaving two motors and a high ratio traction drive transmission;

FIG. 11 is a lever diagram of a continuously variable electricdrivetrain having a motor and a high ratio traction drive transmission;

FIG. 12 is a lever diagram of another continuously variable electricdrivetrain having a motor and a high ratio traction drive transmission;and

FIG. 13 is a flow chart depicting a control process that is used forcontinuously variable electric drivetrains having a motor and a highratio traction drive transmission.

DETAILED DESCRIPTION

It is to be understood that the presently disclosed subject matter mayassume various alternative orientations and step sequences, except whereexpressly specified to the contrary. It is also to be understood thatthe specific devices, assemblies, systems and processes illustrated inthe attached drawings, and described in the following specification aresimply exemplary embodiments of the inventive concepts defined herein.Hence, specific dimensions, directions or other physical characteristicsrelating to the embodiments disclosed are not to be considered aslimiting, unless expressly stated otherwise. Furthermore, preferredembodiments include several novel features, no single one of which issolely responsible for its desirable attributes or which is essential topracticing the embodiments described.

As used here, the terms “operationally connected,” “operationallycoupled”, “operationally linked”, “operably connected”, “operablycoupled”, “operably linked,” and like terms, refer to a relationship(mechanical, linkage, coupling, etc.) between elements whereby operationof one element results in a corresponding, following, or simultaneousoperation or actuation of a second element. It is noted that in usingsaid terms to describe inventive embodiments, specific structures ormechanisms that link or couple the elements are typically described.However, unless otherwise specifically stated, when one of said terms isused, the term indicates that the actual linkage or coupling is capableof taking a variety of forms, which in certain instances will be readilyapparent to a person of ordinary skill in the relevant technology.

It should be noted that reference herein to “traction” does not excludeapplications where the dominant or exclusive mode of power transfer isthrough “friction.” Without attempting to establish a categoricaldifference between traction and friction drives here, generally thesewill be understood as different regimes of power transfer. Tractiondrives usually involve the transfer of power between two elements byshear forces in a thin fluid layer trapped between the elements. Thefluids used in these applications usually exhibit traction coefficientsgreater than conventional mineral oils. The traction coefficient (p)represents the maximum available traction force which would be availableat the interfaces of the contacting components and is the ratio of themaximum available drive torque per contact force. Typically, frictiondrives generally relate to transferring power between two elements byfrictional forces between the elements. For the purposes of thisdisclosure, it should be understood that the transmissions describedhere are capable of operating in both tractive and frictionalapplications based on the torque and speed conditions present duringoperation.

Referring to FIG. 1, in some embodiments, high ratio traction drivetransmissions are characterized by having an arrangement providing aspin free traction roller engagement. High ratio eccentric planetarytraction drive transmissions found in U.S. Pat. No. 8,152,677, fixedratio traction drive transmissions found in U.S. Pat. No. 4,709,589,planetary-roller transmission with elastic roller or ring found in U.S.Pat. No. 4,483,216, and high ratio planetary transmissions found in U.S.Pat. Nos. 4,846,008, and 5,385,514 are illustrative examples aretraction planetary devices implemented herein.

In some embodiments, the traction drive transmission 10 includes atransmission housing 11 provided with a race ring 12 having a racesurface 13. A slightly conical sun roller 14 may be supported on aninput shaft 15 by way of a cam structure 16. Slightly conical planetaryrollers 17 may be supported for orbiting with an output shaft 18. Incertain embodiments, the planetary rollers 17 may be in engagement withthe race ring 12 and the sun roller 14. The cam structure 16 may beconfigured to force the sun roller 14 between the planetary rollers 17to provide traction surface engagement forces depending on the amount oftorque transmitted. As shown, all axial tangents of all the tractionsurfaces intersect in a single point P on the transmission axis so thattrue rolling conditions are provided for all traction surfaces. Thisresults in high-efficiency operation of the transmission and little wearof the traction surfaces.

Referring to FIGS. 2 and 3, in some embodiments, a high ratio tractiondrive transmission 20 includes a sun roller 21 in traction engagementwith a traction roller 22. In some embodiments, the traction roller 22may be supported in a non-rotatable carrier 23. The traction roller 22may be in traction engagement with a traction ring 24. The traction ring24 may be located radially outward of the traction roller 22 and the sunroller 21. In certain embodiments, a ring coupling 25 may be coupled tothe traction ring 24 and configured to transmit rotational power in orout of the high ratio traction drive transmission 20. In someembodiments, the axis of the sun roller 21 may be offset radially withrespect to the rotational center of the traction ring 22 when viewed inthe plane of the page of FIG. 2. In some embodiments, the transmission20 may be provided with a set of floating traction rollers 26 (labeledas “26A” and “26B” in FIG. 3) coupled to the sun roller 21. Thetransmission 20 also may be provided with a set of reaction rollers 27(labeled as “27A” and “27B” in FIG. 3) supported in the carrier 23 bysupport bearings. In some embodiments, the traction roller 22 may besupported in the carrier 23 by a support bearing. In other embodiments,the traction roller 22 may be supported by the sun roller 21 and thereaction rollers 27. During operation of the transmission 20, thereaction rollers 27 provide torque dependent pressure to the floatingtraction rollers 26 which may be transferred to the traction ring 24 andthe traction roller 22 to thereby transmit torque through tractioncontact.

Referring now to FIG. 4, in certain embodiments, a high ratio tractiondrive transmission 30 includes a coaxial input and output shafts 31 and32 rotatably supported in a housing 33 and a housing cover 34.

In some embodiments, the input shaft 31 has a sun roller 35 mountedthereon which forms the center roller of a first planetary tractionroller 36 including a stationary first traction ring 37 arrangedradially outward of the sun roller 35. A set of planetary type tractionrollers 38 may be disposed in the space between the first traction ring37 and the sun roller 35 and in motion-transmitting engagement with bothof them. The planetary traction rollers 38 may be rotatably supported ona first planetary roller carrier 39.

The traction drive transmission 30 includes for each planetary tractionroller 38 a support shaft 40 which may be supported at its free end by asupport ring 41 and on which the planetary traction roller 38 may besupported by a bearing 42.

In some embodiments, the planetary traction rollers 38 include twosections, a first section 38 a and a second section 38 b of differentdiameters. The first section 38 a may be in engagement with the firsttraction ring 37 and the sun roller 35. The second section 38 b may bein engagement with a second traction ring 43, which may be mounted forrotation with the output shaft 32 via a support disc 44.

In some embodiments, the second section 38 b may be coupled to a supportsun roller 45 which may be hollow so that the input shaft 31 may extendtherethrough.

Various axial thrust bearings may be provided for the accommodation ofthe axial forces in the transmission. It may be noted, however, that thesupport shafts 40 of the planetary traction rollers 38 may be arrangedat a slight angle with respect to the axis of the input and outputshafts and that the traction surfaces of the planetary traction rollers38 may be slightly conical. The traction surfaces of the stationaryfirst traction ring 37 and of the rotatable second traction ring 44 maybe correspondingly conical so that the planetary traction rollers 38 maybe forced into the conical space defined by the traction rings uponassembly of the transmission.

Referring to FIG. 5, in some embodiments, an electric axle powertrain100 includes a continuously variable electric drivetrain 102 operablycoupled to a differential 103.

In some embodiments, the differential 103 may be a common differentialgear set implemented to transmit rotational power. The differential 103may be operably coupled to a wheel drive axle 104 configured to drive aset of vehicle wheels 105 (labeled as “105A” and “105B” in FIG. 5).

Referring now to FIG. 6, in some embodiments, a continuously variableelectric drivetrain (CVED) 110 may be optionally configured to be usedin the electric axle powertrain 100. In some embodiments, the CVED 110may be provided with a first combined motor-generator 111 and a combinedsecond motor-generator 112 operably coupled to a high ratio tractiondrive transmission 113. The motor-generators 111, 112 are types ofelectric machines. It should be appreciated that the motor-generators111, 112 may be separate and distinct motor and generator.

In some embodiments, the high ratio traction drive transmission 113includes a ring member 114 in contact with a number of traction rollerssupported in a carrier 115, each traction roller in contact with a sunmember 116.

In some embodiments, the carrier 115 may be configured to transferrotational power out of the CVED 110.

In some embodiments, the first motor-generator 111 may be operablycoupled to the ring member 114.

In some embodiments, the second motor-generator 112 may be operablycoupled to the sun member 116. It should be appreciated that the highratio traction drive transmission 113 may be depicted as a lever diagramto simplify the kinematic relationship between components in the CVED110, and that the high ratio traction drive transmission 113 may beconfigured in a variety of physical forms as described previously.

In some embodiments, the CVED 110 may be provided with multipledownstream gears that provide torque multiplication to the drivenwheels.

In some embodiments, the CVED 110 may be provided with a first transfergear 117 coupled to the carrier 115.

In some embodiments, the first transfer gear 117 couples to a secondtransfer gear 118. The first transfer gear 117 and the second transfergear 118 can be coaxial planetary gear sets or can be transfer geararrangements as depicted in FIG. 6.

Turning now to FIG. 7, an illustrative example of a variogram is showndepicting the range of possible vehicle speeds and axle torques as afunction of the first motor-generator speed (x-axis) and the secondmotor-generator speed (y-axis). During operation of the CVED 110, thefirst motor-generator 111 may be connected to the ring member 114 andmay be a low-speed, high-torque device used in torque-control mode. Thesecond motor-generator 112 may be a high-speed, low-torque deviceconnected to the sun member 116 and used in speed-control mode. Outputof the CVED 110 may be taken from the carrier 115. The high ratiotraction drive transmission 113 functions as a summing planetary andeach motor-generator 111, 112 may be controlled to perform in a peakefficiency region as vehicle speed and power requirements changethroughout operation.

It should be appreciated that the choice of the ring to sun ratio “e₁”for the summing planetary 113 may be selected to account for theasymmetric nature of the motor-generators 111, 112 (either in the speed,torque, or power domain).

Turning now to FIG. 8, in some embodiments, a control process 200 may beelectronically implemented in a controller used for the CVED 110. Fordescription purposes, the control process 200 will reference the CVED110 as an illustrative example.

Those of skill will recognize that the various illustrative logicalblocks, modules, circuits, and algorithm steps described in connectionwith the embodiments disclosed herein, including with reference to thetransmission control system described herein, for example, may beimplemented as electronic hardware, software stored on a computerreadable medium and executable by a processor, or combinations of both.To clearly illustrate this interchangeability of hardware and software,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality.Whether such functionality may be implemented as hardware or softwaredepends upon the particular application and design constraints imposedon the overall system. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the presently disclosed subject matter.

For example, various illustrative logical blocks, modules, and circuitsdescribed in connection with the embodiments disclosed herein may beimplemented or performed with a general purpose processor, a digitalsignal processor (DSP), an application specific integrated circuit(ASIC), a field programmable gate array (FPGA) or other programmablelogic device, discrete gate or transistor logic, discrete hardwarecomponents, or any combination thereof designed to perform the functionsdescribed herein. A general purpose processor may be a microprocessor,but in the alternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration. Software associated with such modules may reside in RAMmemory, flash memory, ROM memory, EPROM memory, EEPROM memory,registers, a hard disk, a removable disk, a CD-ROM, or any othersuitable form of storage medium known in the art. An exemplary storagemedium may be coupled to the processor such that the processor readsinformation from, and writes information to, the storage medium. In thealternative, the storage medium may be integral to the processor. Theprocessor and the storage medium may reside in an ASIC. For example, insome embodiments, a controller for use of control of the CVED 110 aprocessor (not shown).

In some embodiments, a controller (not depicted) of the CVED 110optionally includes an input signal processing module, a transmissioncontrol module and an output signal processing module. The input signalprocessing module may be configured to receive a number of electronicsignals from sensors provided on the vehicle and/or drivetrain. Thesensors may include temperature sensors, speed sensors, positionsensors, among others. In some embodiments, the signal processing modulemay include various sub-modules to perform routines such as signalacquisition, signal arbitration, or other known methods for signalprocessing. The output signal processing module may be configured toelectronically communicate to a variety of actuators and sensors.

The control process 200 begins at a start state step 201 and proceeds toa step 202 where a number of signals may be received. In someembodiments, the signals include a carrier speed ω_(carrier)corresponding to the carrier 115, for example, a ring speed ω_(ring)corresponding to the ring member 114, for example, and a sun speedω_(sun) corresponding to the sun member 116, among other signals forprocessing. In some embodiments, the signals include a wheel speedsignal, a wheel slip status signal from an anti-lock braking module, awheel slip status signal from a traction control module, a signalindicative of a driver demand load, among other signals for processing,and the like, for example.

The control process proceeds to a step 203 where a kinematic carrierspeed ω_(carrier_k) may be determined. In the embodiment shown, thekinematic carrier speed ω_(carrier_k) has a fixed kinematic relationshipto vehicle speed when it may be assumed that there may be no wheel slipto the ground. It is understood, however, that depending on whichcomponent of the high ratio traction drive transmission 113 is driveablycoupled to the first motor-generator 111, which component is driveablycoupled to the second motor-generator 112, and which component is theoutput, the fixed kinematic relationship to the vehicle speed when itmay be assumed that there may be no wheel slip to the ground may be withthe output (i.e. the ring member 114 or the sun member 116) instead ofthe carrier 115 as described hereinafter.

Given that a speed ω_(MG2) of the second motor-generator 112 and a speedω_(MG1) of the first motor-generator 111 may be independent of oneanother, and that the measured and target values are known, slipdiagnostic for the CVED 110 may be available. For example, themotor-generator 111 may be in a speed-control mode with a commandedtarget speed for comparison to the measured speed from a sensor whilethe motor-generator 112 may be in torque-control mode. However, once theoutput speed of the CVED 110 may be known, and it has been determinedthat wheel slip may be not active, and given that the motor-generator111 has a known target speed, the target speed of the motor-generator112 may be calculated form the kinematic relationship through theplanetary for comparison to the measured speed from the sensor. It isunderstood, that the motor-generators 111, 112 may substituted for eachother, and more particularly, the motor-generator 112 may be in aspeed-control mode with a commanded target speed for comparison to themeasured speed from a sensor while the motor-generator 111 may be intorque-control mode. It is further understood that any type of speedsensors may be employed in the control process 200. In some embodiments,the target values may be based on a system or an operator demand.Further, fault isolation to determine the slipping traction interfacemay be also possible.

The step 203 implements a planetary speed constraint to determine thekinematic carrier speed ω_(carrier_k) expressed as the following, wheree₁ may be the ring-to-sun ratio of the high ratio traction drivetransmission 113:

ω_(carrier_k)*(e ₁+1)=ω_(MG2)+ω_(MG1) *e ₁

As a non-limiting example, the kinematic carrier speed ω_(carrier_k) iscalculated based upon the measured speed ω_(MG1), ω_(MG2) of at leastone of the respective motor-generators 111, 112.

In some embodiments, the control process 200 proceeds to a firstevaluation step 204 where the measured carrier speed ω_(carrier) of atleast one of the respective motor-generators 111, 112 received in thestep 202 may be compared with the kinematic carrier speed ω_(carrier_k)determined in the step 203. If the first evaluation step 204 returns atrue result, indicating that the measured carrier speed ω_(carrier) ofat least one of the respective motor-generators 111, 112 may besubstantially equal to the kinematic carrier speed ω_(carrier_k), thecontrol process 200 returns to the step 202. It should be appreciatedthat a CVED 110 transmits torque only when there may be a shear forcedeveloped at a fluid interface. The shear force may only be present whena slip speed occurs across a contact patch. Thus, the CVED 110 may beconstantly experiencing a measurable amount of slip required foroperation of the CVED 110, and the measured carrier speed ω_(carrier) ofat least one of the respective motor-generators 111, 112 may not beexactly equal to the kinematic carrier speed ω_(carrier_k). Therefore, athreshold tolerance may be applied to the speed comparison in step 204such that a false result indicating slip detected occurs only when themeasured carrier speed ω_(carrier) received in the step 202 comparedwith the kinematic carrier speed ω_(carrier_k) determined in the step203 exceeds the threshold tolerance. In some embodiments, the thresholdtolerance may be calibrateable. In certain embodiments, the thresholdtolerance is calculated or determined as a function of traction drivetorque load and traction drive input speed, and thus implemented in alookup table.

If the first evaluation step 204 returns a false result, indicating thatthe measured carrier speed ω_(carrier) may be not substantially equal tothe kinematic carrier speed ω_(carrier_k) and in excess of the tolerancethreshold, the control process 200 proceeds to a step 205 where signalscorresponding to a detected slip state may be transmitted to othermodules of the control system such as a motor control module, a tractioncontrol module, an anti-lock braking control module, and the like, forexample.

In some embodiments, the control process 200 proceeds to a secondevaluation step 206 and a third evaluation step 207 in parallel, i.e.substantially simultaneously. The second evaluation step 206 compares ameasured ring speed ω_(ring) to the speed ω_(MG1) of the firstmotor-generator 111. The third evaluation step 207 compares the measuredsun speed ω_(sun) to the speed ω_(MG2) of the second motor-generator112. The results from the second evaluation step 206 and the thirdevaluation step 207 may be passed to a function step 208 where faultisolation diagnostics may be performed. In some embodiments, thefunction step 208 compares the result of the second evaluation step 206and the third evaluation step 207.

If the second evaluation step 206 passes a true result to the functionstep 208, indicating that the speed ω_(ring) of the ring member 114 maybe substantially equal to the speed ω_(MG1) of the first motor-generator111, and the third evaluation step 207 passes a true result to thefunction step 208, indicating that the speed ω_(sun) of the sun member116 may be substantially equal to the speed ω_(MG2) of the secondmotor-generator 112, the function step 208 returns a true result as adetected damaged gear signal 209. The detected damaged gear signal 209indicates that the source of the detected slip state 205 may bemalfunction or damage to the first transfer gear 117, for example.

If the second evaluation step 206 passes a false result to the functionstep 208, indicating that the speed ω_(ring) of the ring member 114 maynot be substantially equal to the speed ω_(MG1) of the firstmotor-generator 111, and the third evaluation step 207 passes a falseresult to the function step 208, indicating that the speed ω_(sun) ofthe sun member 116 may not be substantially equal to the speed ω_(MG2)of the second motor-generator 112, the function step 208 returns a trueresult as an indeterminant slip signal 210. The indeterminant slipsignal 210 indicates that the source of the detected slip state 205 maybe within the high ratio traction drive transmission 113; however, thefault isolation routine may be unable to determine which tractioncomponent and/or interface may be slipping.

If the second evaluation step 206 passes a false result to the functionstep 208, indicating that the speed ω_(ring) of the ring member 114 maynot be substantially equal to the speed ω_(MG1) of the firstmotor-generator 111, and the third evaluation step 207 passes a trueresult to the function step 208, indicating that the speed ω_(sun) ofthe sun member 116 may be substantially equal to the speed ω_(MG2) ofthe second motor-generator 112, the function step 208 returns a trueresult as a detected ring slip signal 211. The detected ring slip signal211 indicates that the source of the detected slip state 205 may bebetween the ring member 114 and the traction rollers 22 supported in thecarrier 115.

If the second evaluation step 206 passes a true result to the functionstep 208, indicating that the speed ω_(ring) of the ring member 114 maybe substantially equal to the speed ω_(MG1) of the first motor-generator111, and the third evaluation step 207 passes a false result to thefunction step 208, indicating that the speed ω_(sun) of the sun member116 may not be substantially equal to the speed ω_(MG2) of the secondmotor-generator 112, the function step 208 returns a true result as adetected sun slip signal 212. The detected sun slip signal 212 indicatesthat the source of the detected slip state 205 may be between the sunmember 116 and the traction rollers 22 supported in the carrier 115.

In some embodiments, the control process 200 passes signals from thefunction step 208 to a step 213 where commands may be sent to the CVED110 to mitigate the detected slip state 205. For example, commandstransmitted to the CVED 110 may be described in reference to FIG. 10.

It should be appreciated that the evaluation steps implemented in thecontrol process 200 can be configured to compare measured speedsω_(carrier), ω_(ring), ω_(sun) to calibrateable tolerance thresholdsthat account for a known allowable slip between components.

Referring now to FIG. 9, a table 215 summarizes the diagnostic slipstates corresponding to the control process 200. If the carrier speedω_(carrier) from a sensor or calculated via wheel speeds and thering-to-sun ratio disagrees with the kinematic carrier speedω_(carrier_k) calculated from the kinematic relationship to the speedsω_(MG1), ω_(MG2) of at least one of the motor-generators 111, 112, thenthe traction drive may be in a slip state.

$\omega_{{carrier}\_ k} \neq \frac{\omega_{{MG}\; 2} + {\omega_{{MG}\; 1}*e_{1}}}{e_{1} + 1}$

Fault isolation to the slipping contact/interface then requires anadditional sensor to compare another component speed (i.e. the speedω_(ring) of the ring member 114 or the speed ω_(sun) of the sun member116) to the respective speed ω_(MG1), ω_(MG2) of at least one of themotor-generators 111, 112 that may be driving that node.

ω_(ring)≠ω_(MG1) OR ω_(sun)≠ω_(MG2)

Finally, with sensors on all components, an indeterminate slip state canbe detected where both contacts may be slipping.

ω_(sun)≠ω_(MG2) AND ω_(ring)≠ω_(MG1)

Referring now to FIG. 10, in some embodiments, generating commands forslip mitigation may be accomplished by altering a power ratio betweenthe first motor-generator 111 and the second motor-generator 112. Thetorque ratio may be constant and substantially equal to e₁; however,altering a speed set-point of one of the motor-generators 111, 112changes the power ratio between contacting components of the high ratiotraction transmission 113. Because slip may be a strong function ofpower through each contact, an alteration of the power ratio can be usedto mitigate slip. If both the motor-generators 111, 112 may be belowtheir respective base speed and consequently below peak power output,slip mitigation by altering the power ratio between the motor-generators111, 112 while still meeting the current output power demand may bepossible. If it is determined that the slipping component is coupled tothe one of the motor-generators 111, 112 that is in the torque-controlmode, that one of the motor-generators 111, 112 can then be switchedfrom the torque-control mode to the speed-control mode in order toadjust the speed thereof and mitigate the slip state. This isaccomplished by altering the speed command target of the one of themotor-generators 111, 112 that is coupled to the slipping component andin the speed-control mode such that the respective speed ω_(MG1),ω_(MG2) of the one of the motor-generators 111, 112 and hence powerthrough the slipping contact may be reduced. Consequently, the powercarried by the non-slipping contact may be increased. Once both themotor-generators 111, 112 may be above their respective base speeds orspeed of operation for rated torque, the power ratio may be constant andslip mitigation requires a reduction in the output power of the drive. Adamaged gear state determined in step 208 requires that the output powerof the CVED 110 be reduced to zero by disabling the motors.

FIG. 10 depicts a power ratio 220 and a torque ratio 221 versus time 222for a commanded slip mitigation. The commands for slip mitigation may bedependent on operating points of both the motor-generators 111, 112. Ifboth the motor-generators 111, 112 may be below base speed, power ratiobetween the motor-generators 111, 112 can be altered to mitigate slipand still meet drive cycle power demand. For example, the power ratiomay be adjusted from a point 223 to a constant value 224. Operation atthe power ratio corresponding to the constant value 224 does not resultin slip. If the motor-generators 111, 112 may be above base speed, thepower demand at the slipping contact must be reduced and the operator'spower demand may be not met. Similarly, if an indeterminate slip statemay be determined, the total power demand must be reduced.

It should be appreciated that the control process 200 may continuous andtherefore, the steps 202 through 213 of the control process 200 may berepeated as many times as is necessary.

Referring now to FIG. 11, in some embodiments, a continuously variableelectric drivetrain (CVED) 250 includes a motor-generator 251 and a highratio traction drive transmission 252.

In some embodiments, the high ratio traction drive transmission 252 maybe one of the examples provided in FIGS. 1-4.

In some embodiments, the high ratio traction drive transmission 252includes a ring member 253 in contact with a number of traction rollerssupported in a carrier 254, each traction roller in contact with a sunmember 255.

In some embodiments, the motor-generator 251 may be operably coupled tothe sun member 255.

In some embodiments, the carrier 254 may be a grounded member andnon-rotatable.

In some embodiments, the ring member 253 may be configured to transfer arotational power out of the CVED 250.

Referring now to FIG. 12, in some embodiments, a continuously variableelectric drivetrain (CVED) 300 includes a motor-generator 301 and a highratio traction drive transmission 302.

In some embodiments, the high ratio traction drive transmission 302 maybe one of the examples provided in FIGS. 1-4.

In some embodiments, the high ratio traction drive transmission 302includes a ring member 303 in contact with a number of traction rollerssupported in a carrier 304, each traction roller in contact with a sunmember 305.

In some embodiments, the motor-generator 301 may be operably coupled tothe sun member 305.

In some embodiments, the ring member 303 may be a grounded member andnon-rotatable.

In some embodiments, the carrier 304 may be configured to transfer arotational power out of the CVED 300.

Referring now to FIG. 13, in some embodiments, a control process 350 maybe implemented during operation of continuously variable electricdrivetrains having a single motor-generator such as the CVED 250 or theCVED 300. For simplicity of description purposes, the control process350 will be described in reference to the CVED 250 only. It isunderstood, however, that the implementation of the control process 350during operation of the CVED 300 is substantially similar to theimplementation of the control process 350 during operation of the CVED250 described hereinafter.

In some embodiments, the control process 350 begins at a start state 351and proceeds to a step 352 where a number of signals may be receivedsuch as an output speed ω_(output) the CVED 250. The control process 350proceeds to a step 353 where a kinematic output speed ω_(output_k) maybe determined based on the ring-to-sun ratio of the high ratio tractiondrive transmission 252.

The control process 350 proceeds to an evaluation step 354 where themeasured output speed ω_(output) may be compared to the kinematic outputspeed ω_(output_k) determined in the step 353. If the evaluation step354 returns a true result, indicating that the measured output speedω_(output) may be substantially equal to the kinematic output speedω_(output_k) the control process 350 returns to the step 352. If theevaluation step 354 returns a false result, indicating that the measureoutput speed ω_(utput) may not be substantially equal to the kinematicoutput speed ω_(output_k) the control process 200 proceeds to a step 355where a detected slip state signal 355 may be formed and passed to othermodules in the control system for the CVED 250. For example, othermodules may include a motor control module, a traction control module,or an anti-lock braking control module, among others. It should beappreciated that the CVED 250 transmits torque only when there may be ashear force developed at a fluid interface. The shear force may only bepresent when a slip speed occurs across a contact patch. Thus, the CVED250 may be constantly experiencing a measurable amount of slip requiredfor operation of the CVED 250, and the measured output speed ω_(output)of the motor-generator 251 may not be exactly equal to the kinematicoutput speed ω_(output_k). Therefore, a threshold tolerance may beapplied to the speed comparison in step 354 such that a false resultindicating slip detected occurs only when the measured output speedω_(output) received in the step 352 compared with the kinematic outputspeed ω_(output_k) determined in the step 353 exceeds the thresholdtolerance. In some embodiments, the threshold tolerance may becalibrateable. In certain embodiments, the threshold tolerance iscalculated or determined as a function of traction drive torque load andtraction drive input speed, and thus implemented in a look up table.

The control process 350 proceeds to a step 356 where commands may betransmitted to mitigate the slip state. In some embodiments, thecommands for mitigating the slip may be torque commands to themotor-generator 251. Slip mitigation in the single motor embodiments ofFIGS. 11 and 12 requires that the output power of the CVEDs 250, 300 bereduced during slip.

In some embodiments, the commands for mitigating the slip may be powercommands to the motor-generators 251, 301 that can be adjusted based ona torque-control mode or a speed-control mode of the motor-generators251, 301. For example, during a slip state of the CVED 250, 300, themotor-generators 251, 301 can be switched from a torque-control mode toa speed-control mode in order to adjust the speed of themotor-generators 251, 301 and mitigate the slip state. The speed commandtarget may be set such that the motor-generators 251, 301 may becommanded to the correct kinematic speed for a non-slipping state. Themotor-generators 251, 301 can be switched back to torque-control modeonce the CVED 250, 300 may be no longer in a slip state.

It should be appreciated that the control process 350 may be continuousand therefore, the steps 352 through 353 of the control process 350 maybe repeated as many times as is necessary.

It should also be noted that the description above has provideddimensions for certain components or subassemblies. The mentioneddimensions, or ranges of dimensions, may be provided in order to complyas best as possible with certain legal requirements, such as best mode.However, the scope of the embodiments described herein may be to bedetermined solely by the language of the claims, and consequently, noneof the mentioned dimensions may be to be considered limiting on theinventive embodiments, except in so far as any one claim makes aspecified dimension, or range of thereof, a feature of the claim.

While preferred embodiments have been shown and described herein, itwill be obvious to those skilled in the art that such embodiments may beprovided by way of example only. Numerous variations, changes, andsubstitutions will now occur to those skilled in the art withoutdeparting from the preferred embodiments. It should be understood thatvarious alternatives to the embodiments described herein may be employedin practicing the presently disclosed subject matter. It is intendedthat the following claims define the scope of the preferred embodimentsand that methods and structures within the scope of these claims andtheir equivalents be covered thereby.

What is claimed is:
 1. A method of controlling an electric drivetrain,comprising: providing a traction drive transmission including a ringmember, a carrier having a plurality of traction members, and a sunmember; and determining a slip state of the traction drive transmissionbased on a comparison of a speed of at least one of the ring member, thecarrier, the plurality of traction members, and the sun member to akinematic speed of the at least one of the ring member, the carrier, theplurality of traction members, and the sun member.
 2. The method ofclaim 1, wherein the traction drive transmission is operably coupled toat least one motor-generator.
 3. The method of claim 2, furthercomprising switching the at least one motor-generator from atorque-control mode to a speed-control mode in order to mitigate theslip state.
 4. The method of claim 3, further comprising mitigating theslip state of the traction drive transmission by adjusting a speed ofthe at least one motor-generator.
 5. The method of claim 4, furthercomprising switching the at least one motor-generator from thespeed-control mode to the torque-control mode once the traction drivetransmission is no longer in the slip state.
 6. A method of controllinga continuously variable electric drivetrain, comprising: providing afirst motor-generator, a second motor-generator, and a high ratiotraction drive transmission having a ring member, a carrier configuredto support a plurality of traction members, and a sun member, whereinone of the ring member, the carrier, and the sun member is operablycoupled to the first motor-generator, wherein one of the ring member,the carrier, and the sun member transmits a rotational power, andwherein one of the ring member, the carrier, and the sun member isoperably coupled to the second motor-generator; measuring a speed of atleast one of the carrier, the ring member, the sun member, the firstmotor-generator, and the second motor-generator; determining a kinematicspeed of at least one of the carrier, the ring member, the sun member,the first motor-generator, and the second motor-generator based on thespeed of at least one of the first motor-generator and the secondmotor-generator; and determining a slip state of the high ratio tractiondrive transmission based on a comparison of the measured speed of atleast one of the carrier, the ring member, the sun member, the firstmotor-generator, and the second motor-generator to the kinematic speedof at least one of the carrier, the ring member, the sun member, thefirst motor-generator, and the second motor-generator.
 7. The method ofclaim 6, further comprising determining a ring slip based on acomparison of the speed of the ring member to the speed of the at leastone of the first motor-generator and the second motor-generator.
 8. Themethod of claim 6, further comprising determining a sun slip based on acomparison of the speed of the sun member to the speed of the at leastone of the first motor-generator and the second motor-generator.
 9. Themethod of claim 7, further comprising commanding a change in the speedof the at least one of the first motor-generator and the secondmotor-generator based on the ring slip.
 10. The method of claim 8,further comprising commanding a change in the speed of the at least oneof the first motor-generator and the second motor-generator based on thesun slip.
 11. The method of claim 6, further comprising commanding achange in a power ratio between the first motor-generator and the secondmotor-generator based on the slip state.
 12. The method of claim 11,wherein commanding the change in the power ratio includes adjusting thespeed of at least one of the first motor-generator and the secondmotor-generator.
 13. A method of controlling a continuously variableelectric drivetrain, comprising: providing a motor-generator and a highratio traction drive transmission including a sun member, a carrierconfigured to support a plurality of traction members, and a ring memberin contact with the traction members, wherein at least one of the ringmember, the carrier, and the sun member is operably coupled to themotor-generator, wherein at least one of the ring member, the carrier,and the sun member transmits a rotational power, and wherein at leastone of the ring member, the carrier, and the sun member is caused toremain stationary; measuring an output speed of the continuouslyvariable electric drivetrain; determining a kinematic output speed ofthe continuously variable electric drivetrain based on a ring-to-sunratio of the high ratio traction drive transmission; and determining aslip state of the high ratio traction drive transmission based on acomparison of the output speed to the kinematic output speed.
 14. Themethod of claim 13, further comprising mitigating the slip state of thehigh traction drive transmission by adjusting a speed of themotor-generator.